CRISM Instrument, Mission, and Data Set Description

Transcription

1 CRISM Instrument, Mission, and Data Set Description 22 March 2009 Scott L. Murchie and the CRISM team 1

2 Topics to be Discussed Instrument characteristics Hardware overview Data configuration and characteristics Basic instrument operation Observing strategies / campaigns Global Mapping Campaign Atmospheric / Seasonal Change Campaign Targeted Observations Observing modes and observation types Gimbaled: FRT, HRL, HRS, EPF Nadir: MSP, MSW, TOD Calibration pipeline CRISM data set description (EDR, DDR, TRDR, MRDR, CDR) 2

3 CRISM is 1 of 6 MRO Instruments to Map Mars' Surface and Atmosphere CRISM, HiRISE, and CTX characterize surface geologic features MARCI, MCS, and CRISM track spatial and seasonal variations in the atmosphere 3

4 CRISM Hardware Overview 3 cryocoolers keep IR detector at K to control noise Optical Sensor Unit Data Processing Unit controls data acquisition, pixel binning, data editing Gimbal allows observations at multiple geometries to separate surface and atmosphere (±60 along-track) Baffle with 1-time deployed cover cuts out of field stray light Radiator pointing toward evening terminator cools spectrometer optics to - 70C to -80C Gimbal Motor Electronics controls gimbal Internal calibration: shutter for dark measurements, integrating sphere for radiometric calibration Wavelength range !m Spectral sampling 6.55 nm/channel Spatial sampling 18 m/pixel from 300 km 4

5 CRISM Optics 3 shutter positions: open, sphere, closed Detectors are located out of the optical plane 5

6 VNIR Detector ( !m) IR Detector ( !m) 3 Optical "zones" on detector Image brightness Pixel functions 6

7 Basic Structure of the Data: A Cube Composed of Successive Frames Acquired Along Track Wavelength 1 frame Along-track motion Each pixel has a spectrum Successive frames Along slit Each readout of the detector is 1 line of a spatial image. The whole image is built as MRO moves along its ground track. Each pixel has a spectrum whose absorptions can be compared with minerals 7

8 Key Instrument Settings Control the Type of Observation being Taken Primary variables that are set to define observation types These variables are set to manage data volume and to "square" the pixels Pointing Fixed at nadir Track a point and repeatedly scan across it Number of wavelengths All 544 with useful data 3 programmable options (72, 94, or 262 selected wavelengths) for regional/global mapping Frame rate 1 Hz (for internal calibration) 3.75 Hz (hyperspectral observations) 15 or 30 Hz (multispectral mapping) Spatial pixel binning None (18 m) or 2x (36 m) for high-resolution observations 5x (100 m) or 10x (200 m) for global mapping 8

9 First Basic Observation Type: Gimbaled (example shown is Full-Resolution Targeted) Idealized footprints for target at nadir "Targeted" because typically "2 instruments participate "11 images at varying emission angles: "Emission phase function" Central image may be unbinned (18 m/pixel), 2x binned (36 m/pixel), or 10x binned (~180 m/pixel) 1st 5 and last 5 are 10x binned Central high-resolution image for geology; whole set to separate surface/ atmosphere 9

10 Gimbaled Observation Actual Footprints Central swath only Central swath + EPF sequence 10

11 Second Basic Observation Type: Nadir (example shown is Multispectral Survey) Lower-resolution global map to provide context and to find new targets 72 selected wavelengths, 10x-binned spatially to 200 m/pixel Multispectral "noodles" mosaicked to create global map 72 colors 544 colors 1 orbit 3-min segment 11

12 Campaign 1: Multispectral Survey to Provide Global Context and Find Targets This is implemented using nadir pointing, collecting 72 colors at 200 m/pixel. During MRO's Primary Science Phase 55% of Mars was mapped at low atmospheric opacity. 12

13 Campaign 2: Monitor Spatial and Seasonal Variations in Aerosols and Trace Gases Atmospheric water vapor Nadir hyperspectral bursts begin Ls (season) Three types of observations contribute to monitoring the atmosphere A globally distributed grid of fully 10x-binned EPFs every ~9 of Ls measures aerosols and trace gases. The EPFs accompanying targeted observations increase spatial and temporal sampling During the time between targeted observations, EPFs, and mapping observations, periodic bursts of nadir-pointed hyperspectral data monitor trace gases 13

14 Campaign 3: Targeted Observations Directed at High-Priority Sites Locations of targeted observations, overlain on MOLA elevation map 9,514 targeted observations were taken during MRO's PSP. 6,674 were at full resolution (18 m/pixel) and 2,840 were at half resolution (36 m/pixel). The highest concentrations are at phyllosilicate, sulfate, and chloride deposits discovered by OMEGA and THEMIS. 14

15 Campaign 3: Emphasis on Coordination with HiRISE, CTX Mariner 9 CRISM; 18 or 36 m/pixel spectral map White Rock In Pollock Crater As many CRISM observations as possible are taken with coordinated HiRISE and/or CTX images so that both spectral properties and morphology are characterized. 45 km MGS MOC Where data volumes prohibit CRISM hyperspectral targeted observations being coordinated with HiRISE, 100 or 200 m/pixel multispectral data are taken. CTX; 6 m/pixel 30 km HiRISE; 0.3 m/pixel 15

16 Different Types of Observations Result from the Instrument Settings Observing Campaign Targeted Observations Atmospheric Survey Multispectral Survey Gimbal Pointing and Number of Images Gimbal tracks surface with superimposed scan for each image 1 high-resolution image, 10 reduced-resolution EPF images Gimbal track surface with superimposed scan for each image 11 or 13 reducedresolution images Nadir-pointed; multiple images Nadir-pointed; multiple images Observations Type and Description Full resolution targeted Spatial pixels unbinned for target (18 km) Spatial pixels10x binned for EPFs Half resolution short targeted Spatial pixels 2x binned for target (36 km) Spatial pixels10x binned for EPFs Half resolution long targeted Spatial pixels 2x binned for target (36 km; 2x swath length as above) Spatial pixels10x binned for EPFs EPF; spatial pixels 10x binned (~200 km) 9 lon. x 11 lat. grid every ~36 of Ls 27 lon. x 11 lat. grid every ~5 of Ls Tracking Optical Depth Spatial pixels 10x binned (200x900 km) Multispectral survey 72 channels, spatial pixels 10x binned (~200 km) Multispectral windows 72 channels, spatial pixels 5x binned (~100 km) Data Product Nomenclature FRT* HRS* HRL* EPF* TOD* MSP* MSW* Gimbaled Nadir 16

17 Map View / Usage of Different Types of Observations 100 km Gimbaled FRT: 18 m/pixel, 544 channels. High-priority targets. HRS: 36 m/pixel, 544 channels. Where data volume is limited. HRL: 36 m/pixel, 544 channels. Where coverage is more important than high resolution. EPF: images at 180 m/pixel, 544 channels. Free-standing for atmospheric monitoring. Also included with FRT, HRL, HRS. MSP: 200 m/pixel, "72 channels. Long strips for global mapping. 550 km long Nadir MSW: 100 m/pixel, 72 channels. Ride-alongs with HiRISE when data volume is limited. TOD: 180x900 m/pixel, 544 channels. Hyperspectral samples of atmospheric transmission to monitor trace gases. Groundtrack North 17

18 A Collection of Related Images is an "Observation" Unbinned dark images for calibration 10x-binned EPF images Image 00 Images Image 06 The central image is unbinned so this is a Full-Resolution Targeted Observation (FRT) Image 07 File names for all the imags share a unique 8-digit hex target ID, e.g., 00003E12 Each of the images has a unique hex counter in the file name (00, 01,, 0D, 0E) Unbinned dark images for calibration 10x-binned EPF images Image 08 Images 00-0D Image 0E 18

19 All images in all observations: Each Observation is Processed to Multiple Levels Experiment Data Records (EDRs): raw data Shutter-open images aimed at Mars: Targeted Reduced Data Records (TRDRs): calibrated to radiance and I/F Derived Data Records (DDRs): "backplanes" with latitude, longitude, photometric angles, and other information for each image pixel in the TRDRs. Lat/lon support map projection, and photometric angles and ancillary information support correction for illumination and atmospheric effects. Images of the integrating sphere, or dark images embedded within Mars observations: Calibration Data Records (CDRs): matrices used to calibrate scene data. Other CDRs are derived from ground calibrations. NOTE: The calibration process is complicated and users are not recommended to attempt to redo processing themselves. EDRs and CDRs are provided for archival purposes. The main data of interest are TRDRs and DDRs. 19

20 Raw Data Format (EDR) Separate VNIR and IR EDRs A multiband image of raw data formatted from the telemetry stream; assembled from multiple frames A separate ASCII table giving the instrument housekeeping associated with each frame of the data A detached PDS label giving the observation time and setup and the names of the CDRs having information needed to interpret the raw data 20

21 EDR Nomenclature FRT = Class Type FRT (Full Resolution Targeted Observation) HRL (Half Resolution Long Targeted Observation) HRS (Half Resolution Short Targeted Observation) EPF (Atmospheric Survey EPF) TOD (Tracking Optical Depth Observation) MSP (Multispectral Survey) MSW (Multispectral Window) CAL (Generic calibration; internal) ICL (Integrating sphere calibration; internal) FFC (Flat Field Calibration; Mars-pointed) 00003E12 = 8-digit hexadecimal Observation ID 07 = Hex counter for image number within observation SC166 = Activity and the internal command macro used BInnn Bias measurements / Macro# DFnnn Dark field measurements / Macro# SPnnn Sphere measurements / Macro # SCnnn Scene measurements / Macro # L = Sensor ID S for VNIR L for IR EDR0 = EDR, version 0 IMG = file extension IMG for binary image data LBL for detached ASCII PDS label TAB for detached ASCII table of instrument housekeeping (EDR and TRDR only) Observation 3E12 Full-resolution target Counter (central swath = 07) IR detector FRT00003E12_07_SC166L_EDR0: The file name fully describes the type of data, which detector it comes from, the version of the processing, and gives the unique ID and counter Software version 0 21

22 Simplified Calibration Pipeline (1/3) The current version of radiometric calibration is v2 All scene images are calibrated to radiance using internal calibrations to remove time-variable instrumental effects The first correction is to subtract shutter-closed dark measurements from the scene and from a sphere measurement taken close in time The scattered light columns are used to estimate and remove grating glare = Raw scene image, units DN Companion dark image, units DN Corrected scene image, units DN = Raw sphere image, units DN Companion dark image, units DN Corrected sphere image, units DN 22

23 Simplified Calibration Pipeline (2/3) The corrected scene and sphere images are both divided by exposure time to yield values linearly related to radiance The scene is ratioed to the sphere, and multiplied by a ground-based model of the sphere's radiance. The result is scene radiance / exp time Scene radiance, units W m -2 sr -1!m -1 Corrected scene image, units DN Corrected sphere image, units DN / exp time * Ground-based model of sphere radiance, units W m -2 sr -1!m -1 = 23

24 Simplified Calibration Pipeline (3/3) To convert radiance to I/F, the solar flux at 1 AU is convolved with the bandpasses for each CRISM pixel The radiance is divided by the solar flux scaled to Mars' solar distance The result is I/F Scene radiance, units W m -2 sr -1!m -1 * solar distance in AU *! = Solar flux at 1 AU, units W m -2!m -1 Scene I/F, unitless 24

25 Calibrated Data Format (TRDRs) Separate VNIR and IR TRDRs Scene radiance, units W m -2 sr -1!m -1 Scene I/F, unitless Multiband image of radiance; assembled from multiple frames Multiband image of I/F; assembled from multiple frames A separate ASCII table with housekeeping from each frame of the data Detached PDS label for each image, giving the observation time and setup, and all the CDRs used to process the data 25

26 TRDR Nomenclature FRT = Class Type FRT (Full Resolution Targeted Observation) HRL (Half Resolution Long Targeted Observation) HRS (Half Resolution Short Targeted Observation) EPF (Atmospheric Survey EPF) TOD (Tracking Optical Depth Observation) MSP (Multispectral Survey) MSW (Multispectral Window) 00003E12 = 8-digit hexadecimal Observation ID 07 = Hex counter for image number within observation IF166 = Processing and the internal command macro used RAnnn Radiance / Macro# IFnnn I/F / Macro# L = Sensor ID S for VNIR L for IR TRR0 = TRDR, current version = 2 IMG = file extension IMG for binary image data LBL for detached ASCII PDS label TAB for detached ASCII table of instrument housekeeping (EDR and TRDR only) Observation 3E12 Full-resolution target Counter Calibrated to I/F IR detector FRT00003E12_07_IF166L_TRR2: The file name fully describes the type of data, which detector it comes from, the version of the processing, and gives the unique ID and counter Software version 2 26

27 Format of Backplanes (DDRs) Separate VNIR and IR DDRs Core information in the DDRs includes lat, lon, i, e, and g for every pixel, used for map projection and photometric correction Additional information includes elevation, slope magnitude and azimuth, and TES bolometric albedo and thermal inertia for correction of thermal and atmospheric contributions Backplanes, various units Multiband images of backplanes; one-for-one correspondence with spatial position in TRDR A detached PDS label gives the companion observation, its time and setup, and describes each layer of the DDR 27

28 DDR Nomenclature FRT = Class Type FRT (Full Resolution Targeted Observation) HRL (Half Resolution Long Targeted Observation) HRS (Half Resolution Short Targeted Observation) EPF (Atmospheric Survey EPF) TOD (Tracking Optical Depth Observation) MSP (Multispectral Survey) MSW (Multispectral Window) 00003E12 = 8-digit hexadecimal Observation ID 07 = Hex counter for image number within observation DE166 = Processing and the internal command macro used DEnnn Derived information / Macro# L = Sensor ID S for VNIR L for IR DDR1 = DDR, current version = 1 IMG = file extension IMG for binary image data LBL for detached ASCII PDS label Observation 3E12 Full-resolution target Counter Derived information IR detector DDR00003E12_07_DE166L_DDR1: The file name fully describes the companion observation, its type of data, which detector it comes from, and the version of the processing Software version 1 28

29 Usage of DDRs f, = I/F in sensor space Latitude, longitude, incidence, emission, and phase angle Map-projected, photometrically and atmospherically corrected I/F Note: Map convention is planetocentric, positive east longitude 29

30 Mutlspectral Reduced Data Records (MRDRs) CRISM's global multispectral survey mapping exists at the TRDR level as about 64,000 distinct TRDRs each with a companion DDR The data are projected into 1,964 "tiles" organized by Mars charts (MC01-MC30) divided into 5 latitude tiles with variable longitude width 3 parallel products: I/F with backplanes, and the table of included wavelengths Atmospherically corrected Lambert albedo, with backplanes for data used "Summary products" (spectral indices derived from Lambert albedo) 30

31 MRDR Format: I/F Data The most basic version of the MRDRs simply has map-projected I/F, stacked so that lowest incidence angle is on top There is a companion file with DDR information for each strip to support data mining and corrections Multiband image of map-projected I/F (shown with lat/lon grid and overlain on THEMIS day IR) Detached ASCII file giving wavelengths of each band Detached PDS label giving the file history and map projection information 31

32 MRDR Format: Lambert Albedo Data A parallel version has data corrected for photometric and atmospheric effects to "Lambert albedo." There is a companion file with DDR information for each strip to support data mining. There are fewer strips than in the I/F data. Multiband image of map-projected Lambert albedo (shown with lat/lon grid and overlain on THEMIS day IR) Detached ASCII file giving wavelengths of each band Detached PDS label giving the file history and map projection information 32

33 MRDR Format: Summary Product Data The final version includes spectral indices ("summary products") that show variations in absorptions due to mineralogic and atmospheric species. Filtering is applied in sensor space prior to map projection to reduce noise. Multiband image of spectral indices (shown with lat/lon grid and overlain on THEMIS day IR) Detached PDS label giving the file history and map projection information 33

34 MRDR Nomenclature T0750 = Tile number with tile 0000 at the south pole, increasing sprialing east and north MRR = Product Type IF = Subtype of product, e.g. IF I/F DE backplanes for I/F AL Lambert albedo DL backplanes for Lambert albedo SU Summary Products WV List of wavelengths in I/F and Lambert albedo 15 = Planetocentric latitude of upper left corner S = Hemisphere N for north latitude S for south latitude 098 = East longitude of upper left corner 0256 = Resolution, in map-projected pixels per degree 1 = version IMG = file extension IMG for binary image data LBL for detached ASCII PDS label TAB for table of wavelengths Tile number Level of processing Upper left lon Upper left lat N or S hemisphere Scale in ppd T0750_MRRIF_15S098_0256_1.IMG: The file name fully describes the location of the tile, the level of processing, the map scale, and the version of the data 34

35 CDRs Useful for Further Processing: WA Several ground- and flight-derived measurements useful for data processing are stored as CDRs The name of each CDRs includes a 2-letter designation of its type; machine-readable characters indicate the corresponding start time and instrument configuration The WA CDR records "spectral smile," or how each spatial pixel has a slightly different wavelength calibration Sample Wavelength 35

36 CDRs Useful for Further Processing: AT The AT CDR records the scaled atmospheric transmissivity as a function of wavelength Measured using the base and summit of Olympus Mons This is used to correct for attenuation due to atmospheric gases Wavelength Sample 36

37 Caveats to the Current Calibration: "Bad Channels" At boundaries of detector zones, wavelengths with calibration uncertainties can be excluded: VNIR: <410, nm, >1023 nm. IR: <1021 nm, 2694 and 2701 nm, and >3924 nm. IR surrounding 3180 nm if a sharp peak or trough occurs Between-scene comparisons of the following wavelengths are suspect, but intra-scene relative variations are valid: VNIR: <442 nm, " 970 nm IR: <1047 nm, nm >3700 nm Calibration v. 3 (late 2009) will improve some artifacts 37

38 Where to Find More Information Pre-print of CRISM PSP Investigation summary ("Murchie_CRISMPSP_submit.pdf") As-flown Primary Science Phase investigation Intermediate level of detail on instrument and calibration Data processing Data accuracy and precision, and significant artifacts and caveats Also: CRISM Data Set Specification Descriptions of all CRISM data files Pre-print of CRISM instrument paper Description of the instrument and its functions Overview of performance How observations are commanded CRISM Data Product Specification Full detail on contents of all CRISM files Descriptions of all label keywords and housekeeping items Detailed description of radiometric calibration 38